Q: What are these big spiders I’m finding in my house, and are they dangerous?

A: Most spiders in Oregon are not known to be dangerous. Your spider could be a hobo (Tegenaria agrestis) or a giant house spider (Tegenaria duellica).

Both spiders, accidentally introduced from Europe, can be found wherever people live in Oregon. They prefer living in or around homes and they hitchhike on people’s belongings when people move.

They are noticed most often in late summer through early fall, because that’s when the males emerge from their normal shelters in search of females with which to mate. In the home, they’re usually found somewhere on the floor but can also be on walls and ceilings, or in cabinets, tubs and showers. They don’t make obvious webs and are mainly nocturnal in hunting their prey.

It is often very difficult to tell hobo spiders and giant house spiders apart. Adult giant house spiders are larger than hobos, but often examination under a microscope is required to make a definitive identification.

Mostly harmless and beneficial to gardeners, spiders feed on a wide variety of insects and other invertebrates. The hobo spider has a reputation of being dangerous and aggressive, but that is untrue; it’s considered harmless in Europe.

Since symptoms associated with presumed hobo spider bites are not well documented, it is best to treat hobo spiders as if they could cause a medically significant bite.